Architecture is simple: it is that in your landscape that is hard to change. Making design decisions that are wise is the task of an 'architect', which is just another word for 'designer' (though it has been sold as something else). How you organise architecture processes depends on how you organise development, but the subject is the same. For instance, too much yagni is awful: everybody ends up waiting when something is needed that was not clear before. Finding those elements that improve your future speed is part of a good architecture process. Secondly, users are very focused on features and defects, but architecture is potential features and defects, and users are not a good source for those.